I recently read a good write-up on tree structures in PostgreSQL. Hierarchical data is notoriously tricky to model in a relational database, and a variety of techniques have grown out of developers' attempts to optimize for certain types of queries.
In his post, Graeme describes several approaches to modeling trees, including:
In the comments, some users pointed out that the ltree extension could also be used to efficiently store and query materialized paths. LTrees support two powerful query languages (lquery and ltxtquery) for pattern-matching LTree labels and performing full-text searches on labels.
One technique that was not discussed in Graeme's post was the use of closure tables. A closure table is a many-to-many junction table storing all relationships between nodes in a tree. It is related to the adjacency model, in that each database row still stores a reference to its parent row. The closure table gets its name from the additional table, which stores each combination of ancestor/child nodes.
For the past week or two I've been spending some of my spare time working on a web-based SQLite database browser. I thought this would be a useful project, because I've switched all my personal projects over to SQLite and foresee using it for pretty much everything. It also dovetailed with some work I'd been doing lately on peewee regarding reflection and code generation. So it seemed like some pretty good bang/buck, especially given my perception that there weren't many SQLite browsers out there (it turns out there are quite a few, however). I'm sharing it in the hopes that other devs (and non-devs?) find it useful.
In my last post, I wrote about how to work with encrypted SQLite databases with Python. As an example application of these libraries, I showed some code fragments for a fictional diary program. Because I was thinking the examples directory of the peewee repo was looking a little thin, I decided to flesh out the diary program and include it as an example.
In this post, I'll go over the diary code in the hopes that you may find it interesting or useful. The code shows how to use the peewee SQLCipher extension. I've also implemented a simple command-line menu loop. All told, the code is less than 100 lines!
SQLCipher, created by Zetetic, is an open-source library that provides transparent 256-bit AES encryption for your SQLite databases. SQLCipher is used by a large number of organizations, including Nasa, SalesForce, Xerox and more. The project is open-source and BSD licensed. Best of all, there are open-source python bindings.
In this post, I'll show how to compile SQLCipher and the pysqlcipher bindings, then use peewee ORM to work with an encrypted SQLite database.
A while back I wrote about using Flask to create a note-taking app. The goal of that app was to make it really easy for me to save little notes from my phone or computer. In the first follow-up post, I showed how to transition the JSON views to a full-featured RESTful API. I also showed how to add email reminders and to-do lists with checkable items to the notes app. Then in the most recent post, I showed how to leverage SQLite's full-text search extension to make the notes searchable. In this, the final installment, I'll show how I built a command-line client for the note-taking app.
Here is how the notes app looked when we left off at the end of part 3:
If you'd like to follow along, you can find the source code for the most recent version of the note-taking app in this gist:
If you'd rather skip the post and get straight to the code, here is the code for the updated version: